Adoption of solar photovoltaic systems has been increasing in recent years as awareness of the importance of environmental protection grows, for example, international efforts to reduce CO2 emission aiming at preventing global warming. The solar photovoltaic system is configured to allow the solar cell panel to convert the solar energy into DC current. A power conditioner converts the DC current into AC power (commercial power) so as to be used at the respective facilities.
In most of the cases, the solar cell panel has characteristics that a single maximum power point exists with respect to the voltage or current when the solar irradiation and temperature are kept constant, and it is simply increased at the left side of the maximum power point, and simply decreased at the right side of the maximum power point. The aforementioned characteristic of the solar cell panel changes depending on the solar irradiation and temperature. Accordingly, the voltage or current at the maximum power point fluctuates. The power conditioner that relays between the power system and the panel requires the function for searching the maximum output point by controlling the voltage or the current of generated power output from the solar cell panel. This is referred to as a maximum power point tracking (MPPT) function for the solar photovoltaic power generation.
Patent Document 1 or 2 discloses an example of the power conditioner for a generally employed solar photovoltaic power generator system. The maximum power point tracking method as disclosed in Patent Document 1, so called “hill climbing” method fluctuates the voltage or current by a constant amount, and the voltage or current is operated by a constant amount (constant pitch) in the same direction as the positive direction of the power fluctuation, or in the direction opposite the negative direction of the power fluctuation so as to approach the maximum point.
The maximum power point tracking method disclosed in Patent Document 2 makes the optimum operating voltage for obtaining the maximum power constant irrespective of irradiance of light. The optimum operation voltage is derived from the temperature in proportional thereto in reference to a conversion table.